Sounds to me like a simple synthesised sound, play around in a synthesiser using a few different waves, make sure you have the envelope set to have long decay, and then automate the cut-off a high pass filter to create the rise.

It's normally just best to try a few different things in a synthesiser and see what you like.

Hope this is of some help.

Post an example of what you've tried so far, and maybe we can offer suggestions.

Mind posting an example?

Ok, the initial very-high pitch is (the same as) a defibrillator. This is followed by a one-octave sweep of a very basic synth, with some HP Filtering in the middle as @Dominic said, rounded off with some mild static / electric crackle. Should be quite simple to recreate; defib. and electricity samples should be easy to come by.

Good luck!

Sounds like a pretty straight forward synth-sound, having a ring to it that makes me suspect some kind of FM or similar modulating synthesis.

It doesn't have any real fatness, so it's probably not an Ensoniq or Roland, but it does have a rather firm bass, so I doubt it would be a Kawai or Teisco (more or less the same company, but Kawai generally sounds a little firmer but less gritty imho) (I like grit). It also have no sharpness whatsoever, which rules out Moog, Sequential, ARP, Elektron or the analogue KORG-synths. My best guess is that it's from KORG's digital line, or possibly a mid 90's Yamaha SY/DX-synth. I don't know if any of those was the origin to this very sound, but both KORG Wavestation and Yamaha DX-7 II (the first of the DX:es to actually have any lows to speak of) can do that very well.

It might also be a Doepfer A100-system, hard to tell from a more lofi recording. It also seems to have Chorus on it, but I can't tell if it's really added or if it's a phasing in the recording.